1. Field of the Invention
The present invention relates to an object posture calculation system which calculates the relative posture or the relative position and posture between a first object and a second object on the basis of the force acting between the first object and the second object when the first object and the second object are in contact with each other at three contact points.
2. Description of the Related Art
In calculating the relative posture between a first object and a second object, one commonly-known method measures and calculates the relative posture using a noncontact-type sensor such as a camera or a three-dimensional sensor.
When the system used can control the force acting between a first object and a second object, one generally-known method combines the surface of a predetermined portion of the first object with that of a predetermined portion of the second object or fits the first object with the second object to calculate the relative posture between the first object and the second object from the postures at the start and end of operation.
JP H04-043744 B discloses a method for controlling the position of the first object on the basis of a motion model for a compliance mechanism to adjust the force acting between the first object and the second object to a target value.
When the first object and the second object can be fitted together, such a method can fit the first object and the second object together on the basis of the force acting between the first object and the second object to calculate the relative posture between the first object and the second object from the postures at the start and end of operation.
JP H09-091026 A describes a method for calculating a posture error at the approach point by bringing surfaces into contact with each other by pressing with a predetermined force in a plane perpendicular to a hole portion to combine the surfaces with each other, in advance, to correct the posture error.
With this method, the force acting between the first object and the second object is controlled to combine the surface of the first object with that of the second object to calculate the relative posture between the first object and the second object from the postures of the first object at the start and end of operation. A method for correcting the approach point before the fitting operation on the basis of the calculated relative posture is further disclosed.
When the relative posture between the first object and the second object is measured and calculated using a noncontact-type sensor such as a camera or a three-dimensional sensor, the system may get complicated or cost more. In addition, it may be difficult to calculate the relative posture between the first object and the second object, depending on the states of the first object and the second object, such as the position relationship between the first object and the second object, the conditions of interference with surrounding objects, or the surface shapes of the first object and the second object.
When a system which can control the force acting between the first object and the second object is used to calculate the relative posture between the first object and the second object from the postures at the start and end of operation upon fitting of the first object with the second object, the fitting operation involves much time, thus prolonging the cycle time of the system. In addition, the first object and the second object may be preferably fitted together. The first object may be preferably moved for the fitting operation. Problems such as interference with surrounding objects may be encountered upon movement of the first object during the fitting operation. The relative posture between the first object and the second object may not be calculated unless the first object and the second object normally complete their fitting. It is often difficult to fit the first object and the second object together when the relative posture between the first object and the second object is large.
When a system which can control the force acting between the first object and the second object is used to calculate the relative posture between the first object and the second object from the postures at the start and end of operation upon combining of the surface of the first object with that of the second object, the surface combining operation involves much time, thus prolonging the cycle time of the system. In addition, the first object and the second object may preferably have their surfaces combined with each other. The first object may be preferably moved for the surface combining operation. Problems such as interference with surrounding objects may be encountered upon movement of the first object during the surface combining operation.